Old books are cool. I came across a copy of the Companion to the Greek Testament published by Cambridge in 1867. The author is A.C. Barrett. I think editions were published as late as 1887.

I've only looked over the (short) chapter on the text of the New Testament. It is short, concise and quite helpful as an introduction. The brief intros describing different uncial codices are interesting. Here's what they say about Claromontanus:

The Codex Claromontanus (D in the Pauline Epistles) was found in the monastery of Clermont, and is now in the Imperial Library at Paris. It is a Greek-Latin MS containing St. Paul's Epistles, and belongs to the sixth century. Bishop Marsh thought that the Epistle to the Hebrews was added by another transcriber; but Tischendorf, after a careful examination of the MS, has decided that it was written by the same person as the rest of the MS. Dr. Mill supposed it to be the second part of the Codex Bezae, but Wetstein and Bp. Marsh have proved that his opinion is erroneous. It was published by Tischendorf in 1852.

That's it. Short and sweet. Although in later portions of the book, Hebrews is grouped with the Paulines instead of the catholic/general epistles.